QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

FOR THE QUARTERLY PERIOD ENDED SEPTEMBER 30, 2014.

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TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

COMMISSION FILE NUMBER: 814-00757

FS Investment
Corporation

(Exact name of registrant as specified in its charter)

Maryland

26-1630040

(State or other jurisdiction of

incorporation or organization)

(I.R.S. Employer

Identification No.)

Cira Centre

2929 Arch Street, Suite 675

Philadelphia,
Pennsylvania

19104

(Address of principal executive office)

(Zip Code)

Registrants telephone number, including area code: (215) 495-1150

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the
Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90
days. Yes x No ¨.

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every
Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for shorter period that the registrant was
required to submit and post such files). Yes ¨ No ¨.

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller
reporting company. See the definitions of large accelerated filer, accelerated filer and smaller reporting company in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer

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Accelerated filer

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Non-accelerated filer

x (Do not check if a smaller reporting company)

Smaller reporting company

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Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the
Exchange Act). Yes ¨ No x.

Indicate the number of shares outstanding of each of the issuers classes of common stock, as of the latest practicable date.

The issuer has 240,210,060 shares of common stock outstanding as of October 31, 2014.

See Note 8 for a discussion of the Companys credit facilities and unsecured notes. During the nine months ended September 30, 2014 and 2013, the Company paid
$15,653 and $17,844, respectively, in interest expense on the credit facilities.

(2)

See Note 8 for a discussion of the Companys repurchase transaction. During the nine months ended September 30, 2014 and 2013, the Company paid $23,414 and
$16,985, respectively, in interest expense pursuant to the repurchase agreement.

Security may be an obligation of one or more entities affiliated with the named company.

(b)

Certain variable rate securities in the Companys portfolio bear interest at a rate determined by a publicly disclosed base rate plus a basis point spread. As of
September 30, 2014, the three-month London Interbank Offered Rate, or LIBOR, was 0.24%, the Euro Interbank Offered Rate, or EURIBOR, was 0.08% and the U.S. Prime Lending Rate, or Prime, was 3.25%.

Security or portion thereof held within Broad Street Funding LLC and is pledged as collateral supporting the amounts outstanding under the revolving credit facility
with Deutsche Bank AG, New York Branch (see Note 8).

Security or portion thereof held within Locust Street Funding LLC and is pledged as collateral supporting the amounts outstanding under the Class A Notes issued to
Race Street Funding LLC pursuant to an indenture with Citibank, N.A., as trustee (see Note 8).

(g)

Security or portion thereof held within Race Street Funding LLC and is pledged as collateral supporting the amounts outstanding under the repurchase agreement with
JPMorgan Chase Bank, N.A., London Branch (see Note 8).

(h)

Security or portion thereof held within Walnut Street Funding LLC and is pledged as collateral supporting the amounts outstanding under the revolving credit facility
with Wells Fargo Bank, National Association (see Note 8).

The investment is not a qualifying asset under the Investment Company Act of 1940, as amended. A business development company may not acquire any asset other than
qualifying assets, unless, at the time the acquisition is made, qualifying assets represent at least 70% of the companys total assets. As of September 30, 2014, 79.0% of the Companys total assets represented qualifying assets.

(l)

Listed investments may be treated as debt for GAAP or tax purposes.

(m)

Security is non-income producing.

(n)

Security held within IC American Energy Investments, Inc., a wholly-owned subsidiary of the Company.

(o)

Security held within FSIC Investments, Inc., a wholly-owned subsidiary of the Company.

(p)

Security is an unfunded loan commitment.

(q)

Security was on non-accrual status as of September 30, 2014.

(r)

Warrants expire on September 28, 2022 and May 10, 2022 and the strike prices are $121.00 and $100.00 per share, respectively.

(s)

Under the Investment Company Act of 1940, as amended, the Company generally is deemed to be an affiliated person of a portfolio company if it owns 5% or
more of the portfolio companys voting securities and generally is deemed to control a portfolio company if it owns 25% or more of the portfolio companys voting securities or it has the power to exercise control over the
management or policies of such portfolio company. During the nine months ended September 30, 2014, the Company made an investment in and, in connection with such investment is deemed to be an affiliated person of (but would not be
deemed to control), the following portfolio company: